The present invention relates to a contact for a vacuum interrupter, and a vacuum interrupter using the contact.
For obtaining enhanced interrupting performance of the vacuum interrupter, electrodes need to receive arc produced therebetween at interruption (shutoff) by their entire surfaces without concentrating arc onto specific spots. The structure for forming a longitudinal magnetic field between electrodes, i.e. the longitudinal magnetic-field applying method, is adopted to receive arc by the entire surfaces of the electrodes. Generation of the longitudinal magnetic field between the electrodes encloses arc, leading to less loss of charged particles from an arc column, excellent arc stability, restrained temperature rise of the electrodes, and enhanced interrupting performance.
U.S. Pat. No. 4,620,074 (equivalent of Japanese Patent Examined Publication No. Heisei 3(1991)-59531 [=JP3059531B]) describes “a contact arrangement for vacuum switches” adopting the longitudinal magnetic field application method. A contact carrier in a form of a hollow cylinder has an end face which is formed with a contact plate. The contact carrier has a periphery formed with a slit (referred to as “slots” in ABSTRACT). Length (referred to as “predetermined height HT” in ABSTRACT), the number of slits, and an azimuth angle of the slit of the contact carrier are defined with respect to an outer diameter of the contact carrier.
FIG. 15 and FIG. 16 show a construction of a contact of a vacuum interrupter, according to U.S. Pat. No. 4,620,074.
A contact 01 has a contact carrier 02 and a contact end plate 03. The contact carrier 02 has a first end (lower end in FIG. 15) to which the contact end plate 03 is brazed. As a result, the contact 01 is shaped substantially into a cup. The contact carrier 02 has a second end (upper end in FIG. 15) to which a contact plate 04 is brazed. The contact carrier 02 has a periphery which is formed with a plurality of inclined slits 05 each of which is inclined by a predetermined angle. An area between two adjacent inclined slits 05 is defined as a coil part. Moreover, the contact plate 04 is formed with a slit 06 connecting to the inclined slit 05. The slit 06 is offset by a distance b from a center O of the contact 01. As is seen in FIG. 15, there is defined an inclination angle a of the inclined slit 05, relative to an axis of the contact 01. As is seen in FIG. 16, there is defined an azimuth angle β which is an opening angle of the inclined slit 05, with respect to the center O of the contact 01.
The vacuum interrupter using the above contact 01 shows the following features:
A current Ia flowing circumferentially around the contact 01 as is seen in FIG. 15 and a current Ib flowing spirally on the contract plate 04 as is seen in FIG. 16 secure a magnetic flux density between electrodes during current interruption. The magnetic flux density caused by the current Ib shows a concentrated distribution around an axis of the electrode, thereby causing a concentration of arc substantially in the center during the current interruption. The thus concentrated arc disables interruption of a great short circuit.
For interruption of a high voltage and a heavy current, larger coil diameter and greater gap between the contacts are required. In this case, however, the magnetic flux density between the electrodes is likely to become short, thus destabilizing the arc between the electrodes and leading to incapability of interruption.
Moreover, for securing the magnetic field, the azimuth angle β of the inclined slit 05 (formed in the contact carrier 02) needs to be greater. In this case, however, the contact 01 itself may become short in strength. Thereby, opening and closing the contacts 01 may deform the contacts 01, thereby deteriorating voltage withstandability as well as interrupting performance.